Microlithography is used for producing microstructured components, for example integrated circuits. The microlithography process is carried out in what is called a projection exposure apparatus, which includes an illumination device and a projection lens. The image of a photomask (reticle) illuminated by way of the illumination device is in this case projected by way of the projection lens onto a wafer coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the structure of the photomask onto the light-sensitive coating of the substrate.
Mirrors of the projection lens are typically retained in a holding frame (force frame). The mirrors are positioned (in up to three translational degrees of freedom) and spatially oriented (in up to three rotational degrees of freedom) relative to a sensor frame. The sensor frame is configured as a stable frame surrounding the holding frame. Via openings in the holding frame, sensor heads of the sensor frame can be brought closely enough to the mirrors to perform precise measurements with respect to the position and the spatial orientation of the mirrors. One or more mirrors can deteriorate in terms of reflection over the course of their operation and must be interchanged. The sensor frame can here impede the interchanging of deteriorated mirrors.
US 2012/0140241 A1 discloses an approach for mounting the mirrors without a physically stable frame. In this case, six optical longitudinal measurement sections between in each case two neighboring mirrors are described, with which the positions and spatial orientations of the mirrors with respect to one another can be determined. For the longitudinal measurement sections, numerous free visual axes are involved, which are not always available in EUV projection lenses.
U.S. Pat. No. 7,817,248 B2 discloses an optical system, in which optical elements are directly positioned relative to one another using reference elements or indirectly via the holding frame to which the optical elements are attached. The reference elements are here connected to the optical elements.